Disposable absorbent products currently find widespread use in many applications. For example, in the infant and child care areas, diapers and training pants have generally replaced reusable cloth absorbent articles. Other typical disposable absorbent products include feminine care products such as sanitary napkins or tampons, adult incontinence products, and health care products such as surgical drapes or wound dressings. A typical disposable absorbent product generally comprises a composite structure including a topsheet, a backsheet, and an absorbent structure between the topsheet and backsheet. These products usually include some type of fastening system for fitting the product onto the wearer.
Disposable absorbent products are typically subjected to one or more liquid insults, such as of water, urine, menses, or blood, during use. As such, materials of the disposable absorbent products are typically made of liquid-insoluble materials, such as polypropylene films. The films exhibit a sufficient strength and handling capability so that the disposable absorbent product retains its integrity during use by a wearer.
Although current disposable baby diapers and other disposable absorbent products have been generally accepted by the public, these products still have need of improvement in specific areas. For example, many disposable absorbent products may be difficult to dispose of through a toilet or pipes connecting a toilet to the sewer system.
Environmental wellness of disposable absorbent products is becoming an ever increasing concern throughout the world. As landfills continue to fill up, there has been an increased demand for material source reduction in disposable products, the incorporation of more recyclable and/or degradable components in disposable products, and the design of products that may be disposed of by means other than by incorporation into solid waste disposal facilities such as landfills.
As such, there is a need for new materials that may be used in disposable absorbent products that generally retain their integrity and strength during use, but after such use, the materials may be more efficiently disposed of. For example, the disposable absorbent product may be easily and efficiently disposed of by composting. Alternatively, the disposable absorbent product may be easily and efficiently disposed of to a liquid sewage system wherein the disposable absorbent product is capable of being degraded by microorganisms.
Many of the commercially-available biodegradable polymers are aliphatic polyester materials. Although fibers prepared from aliphatic polyesters are known, problems have been encountered with their use. In particular, aliphatic polyester polymers are known to have a relatively slow crystallization rate as compared to, for example, polyolefin polymers, thereby often resulting in poor processability of the aliphatic polyester polymers. Most aliphatic polyester polymers also have much lower melting temperatures than polyolefins and are difficult to cool sufficiently following thermal processing. Aliphatic polyester polymers are, in general, not inherently wettable materials and may need modifications for use in a personal care application. In addition, the use of processing additives may retard the biodegradation rate of the original material or the processing additives themselves may not be biodegradable.
Also, while degradable monocomponent fibers are known, problems have been encountered with their use. In particular, known degradable fibers typically do not have good thermal dimensional stability if a heat-setting process is not employed in the process such that the fibers usually undergo severe heat-shrinkage due to the polymer chain relaxation during downstream heat treatment processes such as thermal bonding or lamination. The actual heat-setting process makes the non-woven process an impracticable method to spin fibers made from this polymer.
For example, although fibers prepared from poly(lactic acid) polymer are known, problems have been encountered with their use. In particular, poly(lactic acid) polymers are known to have a relatively slow crystallization rate as compared to, for example, polyolefin polymers, thereby often resulting in poor processability of the aliphatic polyester polymers. In addition, the poly(lactic acid) polymers generally do not have good thermal dimensional-stability. The poly(lactic acid) polymers usually undergo severe heat-shrinkage due to the relaxation of the polymer chain during downstream heat treatment processes, such as thermal bonding and lamination, unless an extra step such as heat setting is taken. However, such a heat setting step generally limits the use of the fiber in in-situ nonwoven forming processes, such as spunbond and meltblown, where heat setting is very difficult to be accomplished.
Additionally, when producing nonwovens for personal care applications, there are a number of physical properties that will enhance the functionality of the final web. To produce a web comprised of cut fibers, such as an airlaid or bonded carded web, one of the fibrous components must be a binder fiber. To effectively act as a binder fiber, the fibers are usually selected to be homogeneous multicomponent fibers with a significant difference, i.e. at least 20° C., in melt temperature between the higher-melting and the lower-melting components. These fibers may be formed in many different configurations, such as side-by-side or sheath core.
The majority of materials used in personal care applications are polyolefins, which are inherently hydrophobic materials. To make these materials functional, additional post-spinning treatment steps are required, such as surfactant treatment. These extra steps add cost and form a solution which is often not sufficient to achieve optimal fluid management properties.
For personal care applications, one of the most essential properties of nonwoven webs, and their component fibers, are the wetting characteristics. It is beneficial to produce a material that is hydrophilic and permanently wettable. One of the difficulties associated with the current staple fibers is the lack of permanent wettability. Polyolefins are hydrophobic materials which must undergo surfactant treatments to provide wettability. In addition to being only weakly hydrophilic after this treatment, this wettability is not permanent, since the surfactant tends to wash off during consecutive insults.
Accordingly, there is a need for a binder fiber which provides inherent wettability and binding properties. Additionally there is a need for a binder fiber that is biodegradable while also providing these improved wettability and binding properties and yet may be spun without significant heat shrinkage.